Message that appears on the server when I try to put an item in the toolbox using the menu: https://pastebin.com/LfJmQy0z

It works fine in single-player, but on a separate server, the items will seem to vanish until something sync my inventory, like opening an inventory, at which point they're all back where they were and not in the toolbox

Opening the ToolBox via MineMenu wouldn't work well as the box checks if it's in your hotbar... since you open it via a right-click normally. Attempting to do so while it's in your inventory will cause it to not open correctly or... if running vanilla fix... will spam with a bunch of errors while making it not open correctly.

P.S.
If you happen to get around for an update... by any chance would it be possible to show the item stack number? I have... say for example a stack of food in the box but it doesn't tell me how much food I have left exactly.

Thank you for the issue report.

As you may have surmised from my slow reply, I am rather busy.
Synchronising is a pain, but I will see what I can do about this bug and update this issue when I have something. Expect it to happen within the next 30-40 days or so.

Any chance you've had the time to dig into this? I'm having the same issue as I just moved our save game over from single player to a server so I could play the pack with my son. I love this mod but it isn't functioning right now on the server.

Thank you for creating the mod and considering this issue.

I am having a similar issue as well. We appreciate your work! Makes engineering so much smoother.

I'm afraid life has intervened in the meanwhile, and I am unlikely to provide a fix for this anytime soon.

I would suggest looking into MineMenu https://www.curseforge.com/minecraft/mc-mods/minemenu which seems like it can accomplish some of the same tasks, though I don't know if it would fully integrate with the toolbox.

If anyone has the skills to try to solve this, know that the code is open and I will gladly merge a pull request, build, and upload so everyone can enjoy the mod via CurseForge